Efficiency of traditional water wheels

For centuries mankind have used water wheels as a source of mechanical power for mills, weaving factories and machine workshops. By the time the theories and manufacturing methods of water wheels improved; the most developed technology took a significant leap into the turbines at the end of the Nineteenth century and water wheels development ceased. Thanks to a new sensibility to renewable energy and to local and smart electricity production, nowadays the traditional water wheels are regarded again as a clean and accessible way for micro electricity generation from water, especially in presence of very low heads, improving and conciliating the local economy with the local sustainable development. The present work illustrates some theoretical, experimental and numerical results related to a breastshot and an overshot water wheel. Overshot wheels are generally more efficient than breastshot ones and they are particularly suited for sites with small flow rates and high heads, while breastshot wheels are more suited for sites with abundant flow rates and low heads. The calibrated Computational Fluid Dynamic model of the wheels will also give us the possibility of maximizing their mechanical output power and efficiency, by testing different geometries, numbers of buckets and changes in water supply.